So called "rooftop" air conditioning systems have steadily evolved since their introduction in the 1960's for heating and cooling of commercial buildings. Rooftop units are characterized as forced air units that distribute the conditioned air by means of fans, through supply ducts, to each of the ventilated zones of a building. The systems are closed loop systems in the sense that conditioned air is provided to the spaces of a building to cool or heat the spaces, and then is returned by return ducts to the heating or refrigeration system to be heated or cooled again.
The most recent rooftop designs are variable air volume (VAV) systems. VAV systems are designed to operate at a constant supply air temperature, for example, 55.degree. F. The volume of the supply air provided to the ventilated zones of the building is varied in order to satisfy particular cooling or heating requirements. On a hot day, for example, when the zones are fully occupied by people, a high volume of cooled air at 55.degree. F. would be needed to satisfy the cooling requirements. On a cool day, when few people are occupying the building, a substantially reduced volume of cooled air at 55.degree. would be required to meet design cooling requirements. The fans in a VAV system are controlled to vary the volume of conditioned air that is being supplied to the various zones at any given time, thereby keeping the temperature of the zones at a design temperature of, for example, 72.degree. F.
The first VAV air conditioning systems provided all cooling by mechanical means. Thus, the compressor and the evaporator coil were operated frequently in order to cool the air distributed throughout a building. This was true even when the outside ambient air was relatively cool. As ways were sought to improve the efficiency and reduce the cost of cooling air, economizers were designed and installed on air conditioning systems. An economizer is a device that introduces outside air into the system to provide cooling when possible. Since VAV systems always supply air at a constant temperature of nominally 55.degree. F., outside air is effective to assist in cooling at all times that the outside air temperature is less than 55.degree. F.
Outside air is mixed by an economizer in a VAV system with the return air from the building cooling zones. The outside air is provided by the fans as cooled supply air to the ventilated zones in a continuous loop to keep the building at a comfortable temperature of, for example, 72.degree. F. It will be appreciated that, as the temperature of the outside air is reduced, a much reduced volume of outside air is needed to cool the zones to a desired temperature. When the outside air is, for example, 10.degree. F., very little outside air needs to be added to the return air to reduce the return air to 55.degree. F. and to keep the zones at 72.degree. F. In such conditions, the total air flow through the air conditioning system can typically be less than one third of the air conditioning system's full capacity, which occurs during 100% mechanical cooling.
The reduced volume of air flow at the lower outside air temperatures results in a problem called stratification in the supply ducts. This simply means that the return air and the outside air are not mixed together prior to delivery to the cooling zones. When the air in the main supply duct descending into the building becomes stratified, one side of the duct will have return air in it while the other side of the duct has outside air in it. Zones that are supplied off of the "return air" side of the duct receive air that is too warm and such zones are perceived by the occupants as being stale and stuffy. Zones that are supplied off of the "outside air" side of the duct, receive air that is very cool and these zones are perceived by the occupants as being cold and drafty.
The problem of stratification is made worse in the more recent VAV systems that are of a side-by-side' design. Side-by-side VAV systems are designed to have return air enter the rooftop-unit on one side of the unit and the outside air enter on the other side, as opposed to the "over and under" orientation of previous designs. The return air and the outside air each pass through a damper assembly and enter a common plenum, where mixing should occur. Side-by-side designs are preferable in that the air that is directed onto the coils of the evaporator is more uniform in temperature from the top to the bottom of the unit. However, at low air flow rates, the side-by-side design results in the fans drawing the return air and the outside air through the plenum of the rooftop unit in unmixed parallel, side-by-side flows. The air then enters the descending supply ducts in a stratified, unmixed manner. The problem of stratification is further exacerbated as rooftop designs are made wider to add additional cooling capacity. The plenum becomes wider, making it more difficult to effect adequate mixing under low flow conditions.
It is a primary object of the present invention to provide a damper assembly for the economizer of a VAV air conditioning system which accomplishes destratification effectively and efficiently, particularly when the air flow is relatively low.
It is a further object of the present invention to provide such a damper assembly that has a plurality of positionable and controllable sections to effect adequate air flow and mixing under all operating conditions of the air conditioning system operation.
These and further objects of the present invention will become apparent from the following description of the preferred and alternate embodiments.
The present invention provides an air damper assembly for use in an air conditioning apparatus providing conditioned air to a space. The air conditioning apparatus has an outside air portion through which outside air is admitted to the air conditioning apparatus and a return air portion through which return air is admitted to the air conditioning apparatus. The air conditioning apparatus is selectable between a mechanical cooling mode of operation during which the cooling is provided by mechanical means and an outside air cooling mode of operation during which the cooling is provided by admitting outside air to the air conditioning apparatus. The air damper assembly comprises an outside air damper and a return air damper. The outside air damper is for controlling the admission of outside air to the air conditioning apparatus, having a first outside air damper portion that is closed during the outside air cooling mode of operation and having a second outside air damper portion that is at least partially open during the outside air cooling and mechanical cooling modes of operation. The return air damper is for controlling the admission of return air to the air conditioning apparatus, having a first return air damper portion that is closed during the outside air cooling mode of operation and is selectable between the open and closed positions during the mechanical cooling mode of operation, and having a second return air damper portion that is at least partially open during the outside air cooling mode of operation and is selectable between the open and closed positions during the mechanical cooling mode of operation.
The present invention also provides an air damper assembly for use in an air conditioning system that provides conditioned air to a space. The air damper assembly has a return air admitting portion and an outside air admitting portion. The air damper assembly comprises a return air damper sub assembly for controlling the flow of return air and an outside air damper sub assembly for controlling the flow of outside air. The return air damper subassembly defines a return air aperture through which return air flows. The return air damper sub assembly has a first return air aperture control for controlling the opening and closing of a first portion of the return air aperture and a second return air aperture control for controlling the opening and closing of a second portion of the return air aperture. The outside air damper subassembly defines an outside air aperture through which outside air flows. The outside air damper sub-assembly has a first outside air aperture control means for controlling the opening and closing a first portion of the outside air aperture and a second outside air aperture control means for controlling the opening and closing of a second portion of the outside air aperture.
The present invention additionally provides a method of controlling an air conditioning system that supplies conditioned air to a space presenting an air conditioning demand. The air conditioning system has a return air admitting portion and an outside air admitting portion and an air damper assembly. The air damper assembly has a return air damper subassembly that controls the flow of return air. The return air damper subassembly has a first portion and a second portion. The air damper assembly also has an outside air damper subassembly that controls the flow of outside air. The outside air damper subassembly has a first portion and a second portion. The method of promoting a uniform temperature distribution throughout the air conditioning system comprises closing the first portion of the return air damper subassembly and closing the first portion of the outside air damper subassembly and at least partially opening the second portion of the return air damper subassembly and the second portion of the outside air damper subassembly at times of relatively low outside air flow. The method also comprises at least partially opening the second portion of the outside air damper subassembly and varying the first and second portions of the return air damper subassembly between the open and closed positions as a function of outside air temperature and cooling demand at times of relatively high outside air flow.
The present invention further provides a method of controlling an air conditioning system that supplies conditioned at a set conditioned air temperature air to a space presenting an air conditioning demand. The conditioned air is at least partially made up of outside air. The air conditioning system has a return air admitting portion and an outside air admitting portion and an air damper assembly. The air damper assembly having a return air damper subassembly that controls the flow of return air and an outside air damper subassembly that controls the flow of outside air. The return air damper subassembly has a first portion and a second portion. The outside air damper subassembly has a first portion and a second portion, the method of promoting a uniform temperature distribution throughout the conditioned air comprises the steps of: comparing the outside air temperature to the conditioned air temperature; closing the first portion of the return air damper subassembly and the first portion of the outside air damper subassembly at substantially all times when the conditioned air temperature exceeds the outside air temperature; varying the position of the second portion of the return air damper subassembly between the fully closed and the fully open positions as a function of the difference between the outside air temperature and the conditioned air temperature and the air conditioning demand at substantially all times when the conditioned air temperature exceeds the outside air temperature; and, varying the position of the second portion of the outside air damper subassembly between the fully closed position and a partially open position as a function of the difference between the outside air temperature and the conditioned air temperature and the air conditioning demand at substantially all times when the conditioned air temperature exceeds the outside air temperature.
The present invention yet further provides a method of controlling an air conditioning system that supplies conditioned at a set conditioned air temperature air to a space presenting an air conditioning demand, wherein the conditioned air is at least partially made up of outside air. The air conditioning system has a return air admitting portion and an outside air admitting portion and an air damper assembly. The air damper assembly has a return air damper subassembly that controls the flow of return air and an outside air damper subassembly that controls the flow of outside air. The return air damper subassembly has a first portion and a second portion. The outside air damper subassembly has a first portion and a second portion. The method of promoting a uniform temperature distribution throughout the conditioned air comprises the steps of: comparing the outside air temperature to the conditioned air temperature; varying the positions of the first and second portions of the return air damper subassembly between the fully closed position and at least a partially open position at substantially all times when the conditioned air temperature is less than the outside air temperature as a function of the difference between the outside air temperature and the conditioned air temperature and the air conditioning demand; and, varying the positions of the first and second portions of the outside air damper subassembly between the fully open position and at least a partially open position at substantially all times when the conditioned air temperature is less than the outside air temperature as a function of the difference between the outside air temperature and the conditioned air temperature and the air conditioning demand.